Particle filter-sound muffler

ABSTRACT

An inflatable safety cushion device for protecting vehicle passengers that includes a filter-muffler for removing any potentially harmful particles from air flowing into an inflating bag, and for reducing the noise level of the inflating air flow. The filter-muffler comprises a first cylindrical filter element encircling a second cylindrical filter element. A perforated, hexagonal, metallic tube is disposed between the two cylindrical filter elements. The sides of this hexagonal tube cooperate with the inner surface of the outer cylindrical filter element to define six open spaces or chambers. The velocity of air flowing through perforations in the hexagonal element is reduced as the air enters an open chamber. This velocity reduction reduces the noise level of the air flow. The hexagonal element is elastically deflected by a high velocity pulse of air passing through the filter-muffler. This deflection absorbs energy and further reduces the noise level of the air flow.

United States Patent Kasten Nov. 6, 1973 The Bendix Corporation,Southfield, Mich.

Nov. 23, 1971 Inventor:

Assignee:

US. Cl 55/276, 55/463, 55/482 Int. Cl 801d 46/24 Fleld ol Search 55/276,482, 484, 55/486, 489, 510, DIG. 30, 463

[56] References Cited UNITED STATES PATENTS 4/1964 Hobbs 55/DlG. 30 X3,209,857 10/1965 Eckel..." 3,521,429, 7/] 970 Lefiler "SS/276 FOREIGNPATENTS OR APPLICATIONS 882,647 ll/l96l Great Britain 55/482 A PrimaryExaminer-Frank W. Lutter Assistant Examiner- William Cuchlinski, Jr.Att0rneyJohn S. Bell et al.

[57] ABSTRACT An inflatable safety cushion device for protecting vehiclepassengers that includes a filter-muffler for removing any potentiallyharmful particles from air flowing into an inflating bag, and forreducing the noise level of the inflating air flow. The filter-mufflercomprises a first cylindrical filter element encircling a secondcylindrical filter element. A perforated, hexagonal, metallic tube isdisposed between the two cylindrical fllter elements. The sides of thishexagonal tube cooperate with the inner surface of the outer cylindricalfilter element to define six open spaces or chambers. The velocity ofair flowing through perforations in the hexagonal element is reduced asthe air enters an open chamber. This velocity reduction reduces thenoise level of the air flow. The hexagonal element is elasticallydeflected by a high velocity pulse of air passing through thefiltermuffler. This deflection absorbs energy and further reduces thenoise level of the air flow.

5 Claims, 4 Drawing Figures Patented Nov. 6, 1973 3,769,780

All? 6 SUPPL Y 1 PARTICLE FILTER-SOUND MUFFLER BACKGROUND OF THEINVENTION 1. Field of the Invention Filter-muffler devices for filteringand reducing the noise level of a high velocity, pulse type air flowsuch as the flow of air to an inflatable safety cushion for protectingautomobile passengers during a collision.

2. Brief Description of the Prior Art Safety cushions that inflateduring a collision of an automobile to protect passengers are well knownand commonly called safety air bags." The inflatable bag is connected toan air supply which inflates that bag very quickly during a collision.The air supply is separated from an uninflated bag by a metallic wall ordiaphragm which is ruptured in order to initiate inflation of the bag.The rupturing of this metal diaphragm introduces small metallicfragments into the inflating air flow which must be removed from thatflow in order to protect vehicle passengers. In addition, the bag mustbe inflated in such a short time that the air is required to flow. at ahigh velocity that causes thev flow to be extremely'noisy. The noise ofa triggering air bag has been one of the most frequently expressedobjections to the use of these devices.

SUMMARY OF THE INVENTION This invention includes a filter-muffler forremoving any harmful particles from an air or gaseous flow that alsoreduces the noise level of that flow. The filtermuffler comprises afirst cylindrical filter element for removing particles from a gas flowthat isfencircled by a second, larger cylindrical filter element. Theinner diameter of the second filter element is larger than the outerdiameter of the first. A multi-sided perforated tube or conduit isdisposed between the two cylindrical filter elements to hold them in aspaced apart relationship. The sides of the perforated tube cooperatewith the surface of one of the filter elements to define a plurality ofexpansion chambers for receiving gaseous flow passing through theperforated element. The gas expands as it enters an expansion chamber,andthe flow velocity of the gas is reduced. This velocity reductionreduces the noise level of the gas flow. The multi-sided, perforatedtube is formed-from an elastic material that is deflected by a shortduration gaseous flow. This deflection absorbs energy and therebyfurther reduces the noise level of a short duration flow such as a pulseof arr.

The invention also comprises an inflatable safety cushion device orsystem in which the above-described filter-muffler is disposed in aconduit or tube for transmitting air from an air supply to an inflatablebag or cushion. The filter-muffler is disposed in the conduit so thatair flowsin an in-to-out direction through the filter-mufiler into theinflatable safety cushion. The walls of the filter-muffler are porous'sothat air flows into the inflating bag from all positions on thefilter-muffle'r.

The filter-muffler thus diffuses air flowing into the inflating bag andminimizes any possibility that the air portion of. the air flow, theconduit transmits a small flow might rupture the bag. As explainedpreviously,

small metal fragments are introduced into the air flow when the airsupply is triggered to initiate inflation of the safety cushion. Thesepotentially harmful metal fragments are removed from the air flow by thecylindrical filter elements of the above-described filter-.

mufller. The conduit connecting the filter-muffler to portion of the airfrom the air supply directly into the space between the smaller andlarger cylindrical filter elements so that this air need only passthrough the larger cylindrical filter element before entering theinflating safety cushion.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features, andadvantages of this invention, which is defined by the appended claims,will become apparent from a consideration of the following descriptionand the accompanying drawingsin which:

FIG. 1 is a perspective, cutaway view of one embodiment of thefilter-muffler apparatus of this invention;

FIG. 2 is a partially cutaway, plan view of an inflatable safety-cushionsystem that includes the filtermuffler of FIG. 1;

FIG. 3 is an end view of the fllter-muffler and housing of FIG. 2 brokenaway and illustrated from the position defined by line 3-3; and

FIG. 4 is a side view of the filter-mufflerand housing of FIG. 3 cutawayalong line 4-4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates afilter-muffler 10 comprising inner and outer cylindrical filter elements12 and 14 which are held in a spaced apart relationship by a hexagonaltube or conduit 16 having a plurality of slot shaped perforations 18formed therein. The cylindrical filter elements 12 and 14 are radiallywound ribbon-edge type filter elements. Ribbon-edge type filters arewell known porous cylindrical elements. The filters and one method forforming them are described'in my United States Pat. No. 3,496,047assigned to The Bendix Corporation. The sides of the hexagonal tube 16cooperate with the inner surface of cylindrical filter element 12 todefine a plurality of open spaces or'expansion cham'- Bets 20 (seen mostclearly in FIG. 3) having sufficient size so that the velocity of airpassing through perforations 18 will be reduced as that air enters thechambers 20. The noise level of an air flow is reduced as the velocityof that air flow is reduced. The noise level of air flowing through thefilter-muffler 10 is thereby reduced I as that air passes throughperforations 18 to enter the expansion chambers 20.

The hexagonal tube 16 is formed froma material that is sufficientlyelastic to be deformed by a short pulse of air flowing through thefilter-muffler 10. The tube 16, may, for example, be formed from steeland have a thickness on the order of 1/16 inch. The deflection of theforce or impact of air passing through hexagonal element 16 over anumber of the windings of the cylindrical filter 12. Air flow is notdirected against only one or two of those windings as would be the caseif the slots 18 were disposed parallel to those windings, or in otherwords perpendicular to the axis of cylindrical filter elements 12 and14. The 45disposition of the slots 18 thus distributes the force offlowing air across a large number of the windings of the filter element12 and thus minimizes the chance that an air flow might rupture thatfilter element. The 45 disposition of the slots 18 also causeshexagonal-tube 16 to have a high radial strength. That is, these slotsdo not significantly reduce the radial strength of tube 16 as wouldslots disposed parallel to the axis of cylindrical filter elements 12and 14. The disposition of slots 18 at approximately 45 to the axis ofthe muffler 10 thus optimizes the distribution of the'force or impact offlowing air across the windings of filter element 12 and the radialstrength of hexagonal element 16.

FIG. 2 illustrates a complete inflatable safety cushion device 24 thatincludes a high pressure air supply 26, an inflatable air bag 28, and aconduit 30 for transmitting air between the supply 26 and bag 28. Gassupply 26 contains a sufficient supply of air to fully inflate bag 28.This supply is maintained under a high pressure so that bag 28will-inflate very quickly. For example, the gas supply 26 may bepressurized to 3000 lb./sq.in. in order to inflate bag 28 in 50milliseconds. The filtermuffler 10 shown in FIG. 1 is held snugly in aportion 32 of conduit 30 so that air inflating the .bag 28 must firstflow through the filter-muffler. Bag 28 is cemented or otherwiseattached in a substantially leakproof manner to a flange 34 and wrappedaround portion 32 of conduit 30 so that air flowing through thefilter-muffler l inflates that bag. A thin wall or diaphragm 36separates the gas stored in supply 26 from bag 28. A small explosivecharge 38 for rupturing diaphragm 36 to initiate inflation of bag 28 isdisposed on one side of that diaphragm. Explosive charge 38 is connectedso that it will be triggered by a. collision of the vehicle in which thesafety device 24 is mounted.

'In "operation, explosive charge 38 is detonated by a collision of 'th'evehicle in which safety device 24 is mounted. The explosion of thischarge ruptures disc 36, which allows'air to flow from supply 26 intobag 28. However, fragments of disc 36 are introduced into the air flow.These fragments are removed from the air flow by filter elements 12 and14 which prevent them from reaching and injuring any vehicle passenger.Air

from supply 26 flowing into muffler sees the entire cross section ofthat muffler illustrated in FIG. 3. The major portion of the air fromsupply 26 flows into the center of filter 14 which removes metalfragments from the flow. Air flows from the center or core of filterelement 14 through that element and through the perforations 18 of tube16 into expansion chambers 20. Air flowing through the slots orperforations l8 expands upon entering chambers 20.'The velocity of anair flow reduces as the air expands. This velocity reduction isaccompanied by a reduction in the noise level of the air flow. The airflow also causes hexagonal element 16 to elastically deform. Thisdeformation absorbs energy from the air flow and thus further reducesthe noise level of that air flow.

flow into the center of filter element 14, but instead flows directlyinto the open spaces or chambers between elements 12 and 14. Thefilter-muffler 10 provides a large reduction in the noise level of theair flowing from supply 26 into bag 28 even though the entire flow doesnot pass through elements 14 and 16. The air flowing directly into thearea between filter elements 12 and 14 diffuses or disperses the airflowing through filter element 14 and slots 18 and causes air to flowthrough each portion of filter 12 into bag 28. This dispersion minimizesthe possibility that an air flow may cause either filter 12 or bag 28 torupture. In addition, the flow resistance encountered by air from supply26 is minimized because all air from that supply is not required to flowthrough all three elements 12, 14, and 16. Filter element 12 removes anymetal fragments or other particles from the air flow that does not passthrough element 14 so that no metal fragments are allowed to reach orinjure a passenger.

Having thus described one embodiment of this invention, a number ofmodifications will occur to those skilled in the art. Therefore, what isclaimed is:

1. A device for providing a filtered gaseous flow having a low noiselevel comprising:

a first cylindrical filter element for receiving and removing particlesfrom said gaseous flow;

a second cylindrical filter element encircling said first filterelement, said second filter element having sufficient strength towithstand a predetermined gas flow and an inner diameter larger than theouter diameter of said first element;

a multi-sided, perforated element disposed between said first and secondcylindrical filter elements maintaining said filter elements in a spacedrelationship with respect to each other, the sides of said perforatedelement cooperating with the surface of at least one of said filterelements to define a plurality of expansion chambers for receivinggaseous flow passing through the perforations'of said perforatedelement, the velocity andthereby the noise level of said gaseous flowbeing reduced upon entering said expansion chambers; and

end closure means for directing received gas flow in a radial directionthrough said cylindrical and multi-sided elements.

2. The device of claim 1 in which said multi-sided element is formedfrom an elastic materialvthat is deflected by a short duration gaseousflow, said deflection absorbing energy and thereby further reducing thenoise level of said short duration flow.

3. The device of claim 2 in which:

said first filter element and said second cylindrical element eachcomprise radially would ribbon-edge type filter elements; and

the perforations in said perforated element comprise narrow slotsdisposed at substantially 45 to the axis of said cylindrical elements,said 45 disposition of said slots optimizing the radial strength ofsaidperforated element and the distribution across the surface of one ofsaid cylindrical filter elements of the force of the gaseous flowpassing through said slots.

4. The device of claim 3 wherein said end closure means comprises adeformable end plug disposed at one end of said first cylindrical filterelement to absorb energy from said short duration gaseous flow andthereby reduce the noise level of said flow.

at least one of said filter elements to define said plurality ofexpansion chambers for receiving gaseous flow passing through theperforations of said perforated element, the velocity and thereby thenoise level of said gaseous flow being reduced upon entering saidexpansion chambers;

end closure means for directing gas flow in a radial direction throughsaid cylindrical and multi-sided 7 elements; and

housing means having a predetermined strength for containing saidcylindrical and said multi'sided elements.

1. A device for providing a filtered gaseous flow having a low noiselevel comprising: a first cylindrical filter element for receiving andremoving particles from said gaseous flow; a second cylindrical filterelement encircling said first filter element, said second filter elementhaving sufficient strength to withstand a predetermined gas flow and aninner diameter larger than the outer diameter of said first element; amulti-sided, perforated element disposed between said first and secondcylindrical filter elements maintaining said filter elements in a spacedrelationship with respect to each other, the sides of said perforatedelement cooperating with the surface of at least one of said filterelements to define a plurality of expansion chambers for receivinggaseous flow passing through the perforations of said perforatedelement, the velocity and thereby the noise level of said gaseous flowbeing reduced upon entering said expansion chambers; and end closuremeans for directing received gas flow in a radial direction through saidcylindrical and multi-sided elements.
 2. The device of claim 1 in whichsaid multi-sided element is formed from an elastic material that isdeflected by a short duration gaseous flow, said deflection absorbingenergy and thereby further reducing the noise level of said shortduration flow.
 3. The device of claim 2 in which: said first filterelement and said second cylindrical element each comprise radially wouldribbon-edge type filter elements; and the perforations in saidperforated element comprise narrow slots disposed at substantially 45*to the axis of said cylindrical elements, said 45* disposition of saidslots optimizing the radial strength of said perforated element and thedistribution across the surface of one of said cylindrical filterelements of the force of the gaseous flow passing through said slots. 4.The device of claim 3 wherein said end closure means comprises adeformable end plug disposed at one end of said first cylindrical filterelement to absorb energy from said short duration gaseous flow andthereby reduce the noise level of said flow.
 5. A device for providing afiltered gaseous flow having a low noise level comprising: a firstcylindrical filter element for receiving and removing particles fromsaid gaseous flow; a second cylindrical filter element encircling saidfirst filter element, said second filter element having an innerdiameter larger than the outer diameter of said first element; amulti-sided, perforated element disposed between said first and secondcylindrical filter element for maintaining said filter element in aspaced relationship with respect to each other, the sides of saidperforated element cooperating with the surface of at least one of saidfilter elements to define said plurality of exPansion chambers forreceiving gaseous flow passing through the perforations of saidperforated element, the velocity and thereby the noise level of saidgaseous flow being reduced upon entering said expansion chambers; endclosure means for directing gas flow in a radial direction through saidcylindrical and multi-sided elements; and housing means having apredetermined strength for containing said cylindrical and saidmulti-sided elements.